Ran into a funky issue recently with Internet Explorer, YouTube embeds and duplicate closed captions (CC)
Videos that you use closed captions (CC) on work fine in Chrome, Firefox, even Microsoft Edge, but some videos, some times, in some areas of the video would duplicate closed captions in Internet Explorer 11.
The fix for this is to use an iframe embed for Internet Explorer and you will no longer see duplicated CCs. The more you know!
Steve Novoselac's Blog 